Nutritional Myths :: BUSTED!

Article by James Collier BSc (Hons) RNutr, Nutrition Consultant

Dubious health claims from unscrupulous 'experts' are vast and a major bugbear of mine. However you don't only hear these touted 'facts' from self proclaimed gurus, but also from product companies and even the Government. These far fetched claims stem from the easily rubbished, like the one 'Cigarettes help you breathe more easily' (pushed by a tobacco company in post-war America), to the seemingly plausible, like skipping meals will help you lose weight (it won't, as small regular meals will help speed up the metabolism and aid weight loss).

Nutritional claims have been made for centuries. Chinese medicine is a great example; there are loads of Chinese herbs which 'cure' certain conditions, but do they all work? Some have been explored through conventional clinical trials, with variable results, indicating some do, though unfortunately, most do not. New claims appear every week in faddy diet magazines and daytime TV programmes, many by self proclaimed nutrition experts with no scientific basis. Let's explore just a few of the more popular nutritional myths throughout history and see if there is any credibility in them, or if we can debunk them completely.

'Don't eat after 6.00pm if you're trying to lose weight'

You often hear diet promoters saying don't eat after 5.00, 6.00 or 7.00pm if you want to lose weight. Who knows how they can specify an hour as we all go to bed at different times! The idea behind this stems from blood levels of the hormone insulin which is higher in the evening than after waking, so you're more likely to lay food down as fat later in the day. However the actual effect of this is very small and other factors also affect insulin levels, like what and when we eat and exercise. Plus it's more important to eat small amounts of slowly digested carbohydrate foods at regular intervals through the day as this will help keep a faster metabolism and a faster metabolism is an asset in losing weight. Obviously don't eat too much last thing at night, as it's bad for digestion to lie down on a full stomach, but otherwise, there's nothing wrong with eating after 6.00pm.Verdict: myth

'Celery has Negative Calories'

The concept of negative calories is due to the fact that celery and other high fibre salad veg, including lettuce, have a very low calorie value and involve considerable chewing and digestion, and the energy cost of digestion involves a higher calorie expenditure than the calorie value of celery. However this is not correct and there is a whole lot more which goes on in our complex digestive systems. We all have healthy gut flora (bacteria) living in our intestines which help us digest our food. Some of our gut flora bacteria can actually process some of the polysaccharide fibre from these foods and turn it into mono- and disaccharide breakdown products which we can then absorb and use for energy. The amount of energy that this actually produces in real terms though is very little, and is roughly equal to the cost of digesting fibrous foods. So the cost of digesting celery is about equal to what the flora produce form the fibre, so, whilst there is no significant energy value from celery, celery doesn't have so called 'negative calories'. Nevertheless, it's a great healthy high fibre food which should be included in your diet, and don't forget it will help fill you up and stop you from snacking, therefore helping you to control your weight indirectly.Verdict: myth

'Grapefruits burn fat'

Most serious dieters at one time or another have been told to eat grapefruit. This claim stems from The Grapefruit Diet, originally called The Hollywood Diet, which started in the 1930s and has come back in various forms many times since then. Dieters on this diet are permitted a few vegetables, tiny amounts of protein and lots of grapefruit, from the belief that grapefruit contains a special fat-burning enzyme. The only study conducted was performed by Johns Hopkins University in Baltimore1, and interestingly on behalf of and sponsored by the Florida Citrus Department! Subjects were asked to consume two servings of Florida grapefruit or grapefruit juice each, and lost good weight. But the results weren't particularly valuable in proving whether grapefruit works as a weight-loss aid because, as with many other fad diets, it is because dieters simply limit their calorie intake. As soon as you come off the diet, you will gain weight again because firstly these diets do nothing to change long term eating habits and secondly the body interprets a crash diet so low in calories as starvation, hence the body compensates by slowing down metabolism to conserve all available energy. This lowered level of metabolism makes future weight loss much more difficult.

Grapefruit has no active properties that help burn fat. They are healthy, high in fibre and micronutrients and a low calorie food that makes a good addition to any healthy diet, as should other fruits and vegetables.Verdict: myth

'Carrots will make you see in the dark'

My Grandma used to say this to me, and like any kid, I believed her, even though I loathed carrots! Obviously this isn't true; if you eat carrots you'll develop some super power and be able to see in the dark? Well, it doesn't work to this extreme, but there is some truth in it. Carrots are high in beta-carotene, which as well as being an antioxidant, is a pre-cursor to vitamin A, i.e. retinol. Retinol is involved in the production of an eye pigment called rhodopsin which is synthesised in the retina by rods when we look into darkness. Therefore retinol is essential for night-vision and a deficiency in vitamin A does indeed result in complete night blindness. So although eating your carrots up may not literally make you able to see in the dark, a good intake of carrots in your diet will make a valuable contribution to helping night-vision.Verdict: some truth

'Brown Bread is more Nutritious than White'

Brown bread is merely brown coloured white bread and contains the same amount of fibre as white bread, i.e. nearly zero! However, wholemeal and granary bread are more nutritious being high in fibre and B vitamins.Verdict: myth

'Eating your crusts will make your hair curl'

I don't know where this one came from, but I do know...Verdict: myth

'Guinness for Strength'

The famous 'Guinness is good for you' and similar advertisements from the 1930s – you'll have seen these. Back in those days there was little or no regulation on marketing and food companies could almost say whatever they wanted to. Guinness does conjure up this image of a 'real man's drink' though, even today. Is this valid? Well not really, it's not even notably high in iron with cider having a higher iron content. So, whilst Guinness may make you feel manly, it doesn't give you strength!Verdict: myth

'Eating more than 2-3 eggs per week will lead to high blood cholesterol levels'

Eggs do contain cholesterol. However, the cholesterol we eat has little or no effect on your blood cholesterol level as cholesterol is synthesised from within the body. The quality of eggs varies, and if you're getting locally produced free range eggs where the chickens have been fed on quality grain and bugs and flies from around the farmyard, these eggs are a really healthy food. It's whole diet which affects blood cholesterol level; just keep off junk and processed foods and don't worry about eggs.Verdict: myth

'Warm milk before bed will help you sleep better'

Another old wives tale and again not completely devoid of truth. Serotonin is the so called 'happy hormone' secreted in the brain which promotes mood elevation and relaxation. High levels of serotonin help you feel calmer and help you fall asleep and improve sleep quality. Serotonin has a very high concentration of the amino acid tryptophan, and a good intake of tryptophan helps serotonin synthesis. Milk protein is rich in tryptophan, but the complex structure of milk means it's often hard to digest the protein and free up tryptophan easily. However, warming milk, helps break down the protein structure, and frees up tryptophan to digestive enzymes. Therefore warm milk does help increase blood tryptophan concentrations, which helps increase serotonin, which in turn helps us relax.Verdict: true

These are just some nutritional myths touted over the years. There are, of course, many, many more, some of which have claims which seem very credible. I wonder, if I were to write this article in, say, 20 years, what I'd be including. Would there be some new ones on the list? Are some of the claims being made today soon to be refuted…? Food for thought (to end with a nutrition-related pun!)